(Invited) A Solid-State Chemistry Perspective of Layered Oxide Cathodes for Lithium-Ion Batteries

Abstract

The discovery of layered, spinel, and polyanion oxide cathodes for lithium-ion batteries in the 1980s has aided a significant increase in the cell voltage and energy density of lithium-ion batteries. Among them, the layered LiMO2 oxides are at the forefront for portable electronics and electric vehicle applications. Although 40 years have passed by after their initial discovery, we are still in the process of learning and understanding the intricacies of the solid-state chemistry associated with them, particularly at high nickel contents. Cycle, thermal, and air instabilities are the major hurdles in employing ultrahigh-nickel layered oxide cathodes in practical cells. Phase transitions, cracks, aggressive surface reactivity with the organic electrolyte or ambient air, transition-metal-ion dissolution and migration to the anode, and consequent degradation of the anode are some of the major challenges. Cationic doping and surface conditioning are pursued to overcome some of the challenges, but largely on a trial and error process.This presentation will focus on a solid-state chemistry perspective of the intricacies of layered oxide cathodes with high-nickel contents with various dopants. A fundamental understanding of the following factors will be provided: the role of different dopants in terms of their site occupancy and bulk vs. surface decoration, the dominant degradation factors, the origin of transition-metal ion dissolution, role of electrolyte additives, etc. The understanding is developed based on specifically designed cathode compositions and in-depth characterizations of the cathodes and anodes after extensive cycling, employing a variety of advanced characterization methodologies, such as in-situ x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), time of flight – secondary ion mass spectrometry (TOF-SIMS), and high-resolution transmission electron microscopy (HR-TEM). The understanding developed is used to design and scale-up robust high-nickel layered oxide cathodes with low or no expensive cobalt in them.